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Journal of Virology, May 2008, p. 4471-4479, Vol. 82, No. 9
0022-538X/08/$08.00+0 doi:10.1128/JVI.02472-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.
Severe Acute Respiratory Syndrome Coronavirus nsp1 Suppresses Host Gene Expression, Including That of Type I Interferon, in Infected Cells
Krishna Narayanan,
Cheng Huang,
Kumari Lokugamage,
Wataru Kamitani,
Tetsuro Ikegami,
Chien-Te K. Tseng, and
Shinji Makino*
Department of Microbiology and Immunology, The University of Texas Medical Branch at Galveston, Galveston, Texas 77555-1019
Received 16 November 2007/
Accepted 15 February 2008
The severe acute respiratory syndrome coronavirus (SARS-CoV) nsp1 protein has unique biological functions that have not been described in the viral proteins of any RNA viruses; expressed SARS-CoV nsp1 protein has been found to suppress host gene expression by promoting host mRNA degradation and inhibiting translation. We generated an nsp1 mutant (nsp1-mt) that neither promoted host mRNA degradation nor suppressed host protein synthesis in expressing cells. Both a SARS-CoV mutant virus, encoding the nsp1-mt protein (SARS-CoV-mt), and a wild-type virus (SARS-CoV-WT) replicated efficiently and exhibited similar one-step growth kinetics in susceptible cells. Both viruses accumulated similar amounts of virus-specific mRNAs and nsp1 protein in infected cells, whereas the amounts of endogenous host mRNAs were clearly higher in SARS-CoV-mt-infected cells than in SARS-CoV-WT-infected cells, in both the presence and absence of actinomycin D. Further, SARS-CoV-WT replication strongly inhibited host protein synthesis, whereas host protein synthesis inhibition in SARS-CoV-mt-infected cells was not as efficient as in SARS-CoV-WT-infected cells. These data revealed that nsp1 indeed promoted host mRNA degradation and contributed to host protein translation inhibition in infected cells. Notably, SARS-CoV-mt infection, but not SARS-CoV-WT infection, induced high levels of beta interferon (IFN) mRNA accumulation and high titers of type I IFN production. These data demonstrated that SARS-CoV nsp1 suppressed host innate immune functions, including type I IFN expression, in infected cells and suggested that SARS-CoV nsp1 most probably plays a critical role in SARS-CoV virulence.
* Corresponding author. Mailing address: Department of Microbiology and Immunology, The University of Texas Medical Branch at Galveston, Galveston, TX 77555-1019. Phone: (409) 772-2323. Fax: (409) 772-5065. E-mail:
shmakino{at}utmb.edu
Published ahead of print on 27 February 2008.
K.N., C.H., and K.L. contributed equally to this study.
Journal of Virology, May 2008, p. 4471-4479, Vol. 82, No. 9
0022-538X/08/$08.00+0 doi:10.1128/JVI.02472-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.
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